It is useful for various medical diagnostic purposes to utilize a reflectance spectroscope to analyze samples of body fluid, for example, to determine the color of a person's urine or blood. As is known, spectroscopy uses the linear relationship between absorbance and concentration of an absorbing species (Beer's law), to determine the contents of a sample. An unknown concentration of an analyte can be determined by measuring the amount of light that a sample absorbs and applying Beer's law. If the absorptivity coefficient of the analyte is not known, the unknown concentration can be determined using a working curve of absorbance versus concentration derived from standards.
For example, immunoassay is a technology for identifying and quantifying organic and inorganic compounds. Immunoassay uses antibodies that have been developed to bind with a target compound or class of compounds. The technology has been used widely because the antibodies can be highly specific to the target compound or group of compounds and because immunoassay kits are relatively quick and simple to use. Concentrations of analytes are identified through the use of a sensitive colorimetric reaction. The determination of the target analyte's presence is made by comparing the color developed by a sample of unknown concentration with the color formed by the standard containing the analyte at a known concentration. The concentration of the analyte is determined by the intensity of color in the sample. The concentration can be estimated roughly by the naked eye or can be determined more accurately with a reflectance spectroscope.
Reflectance spectroscopy is the study of light as a function of wavelength that has been reflected or scattered from a solid, liquid, or gas. A conventional reflectance spectroscope may determine the color of a liquid sample, such as urine or blood, disposed on a white, non-reactive pad by illuminating the pad and taking a number of reflectance readings from the pad, each having a magnitude relating to a different wavelength of visible light. The color of the sample on the pad may then be determined based upon the relative magnitudes of red, green, blue and infrared reflectance signals. Reagent pads can be provided with different reagents which cause a color change in response to the presence of a certain type of constituent in urine, such as leukocytes (white blood cells) or red blood cells. A reagent strip may have ten or more different types of reagent pads, for example. Immunoassay strips or cassettes may also be used with other types of liquid samples, such as blood.
U.S. Pat. No. 5,654,803, which is assigned to the assignee of the present disclosure, discloses an apparatus and method for determination of non-hemolyzed levels of occult blood in urine using reflectance spectroscopy. The apparatus is provided with a light source for successively illuminating a plurality of different portions of a reagent pad on which a urine sample is disposed, and a detector array for detecting light received from the reagent pad and generating a plurality of reflectance signals in response to light received from a corresponding one of the different portions of the reagent pad. The apparatus is also provided with means for determining whether the magnitude of one of the reflectance signals is substantially different than the magnitude of another of the reflectance signals. Where the body-fluid sample is urine, this capability allows the apparatus to detect the presence of non-hemolyzed levels of occult blood in the urine sample.
U.S. Pat. No. 5,877,863, which is also assigned to the assignee of the present disclosure, shows an optical inspection apparatus for inspecting a liquid sample, such as urine, using reflectance spectroscopy. The apparatus includes a readhead for illuminating a target area substantially uniformly via only a single light-emitting diode for each wavelength of interest and receiving light from the target area so that reagent tests may be performed. The readhead is provided with a housing, first and second light sources mounted in a fixed position relative to the housing, a light guide mounted to receive light from each of the light sources which conveys, when only one of the light sources is illuminated, substantially all of the light from the light source to illuminate a target area substantially uniformly, and a light detector coupled to receive light from the target area. Each of the first and second light sources is composed of only a single light-emitting diode for emitting substantially monochromatic light of a different wavelength.
Fluorescence spectroscopy is the study of light that has been absorbed at one wavelength and re-emitted at a different wavelength (e.g., fluorescent light is re-emitted by a sample of body fluid in response to a light having a specific wavelength, such as ultraviolet light, being directed at the sample). It is useful for various medical diagnostic purposes to use fluorescence detection to analyze samples of body fluid, for example, to determine a level of glucose in a patient's blood or urine, or to determine a pH level of the patient's blood or urine. U.S. Pat. No. 6,232,609 to Snyder et al., for example, shows an apparatus for glucose monitoring. The glucose monitor illuminates a sample with water with ultraviolet excitation light that induces the water and any glucose present in the sample to emit return light that includes Raman scattered light and glucose emission or fluorescence light. The return light is monitored and processed using a predictive regression model to determine the concentration of glucose in the sample. The predictive regression model accounts for nonlinearities between the glucose concentration and intensity of return light within different wavelength bands at a predetermined excitation light energy or the intensity of return light within a predetermined wavelength band at different excitation energy levels. A fiber-optic waveguide is used to guide the excitation light from a laser excitation source to the sample and the return light from the sample to a sensor.
What is still desired is a new and improved apparatus and method for performing tests on a sample of body fluid and, more particularly, to a readhead for use with the apparatus. Preferably the readhead will include components for conducting both fluorescence spectropy and reflectance spectroscopy.